Polyurethane adhesive thermoforming lamination process employing water-based

ABSTRACT

This invention presents new water-based adhesives suitable for use in thermoforming lamination systems. More particularly, this invention presents water-based adhesive-forming compositions comprising an aromatic polyurethane in water dispersion or emulsion and a compatible cross-linking agent; also includable in the compositions are thickening agents and pigments. These new adhesives, it has been found, exhibit bonding strengths and temperature resistance far superior to the solvent and water-based adhesives currently used in industrial applications, and are useful in thermoforming lamination processes. Also disclosed is a one-step thermoform lamination edge-folding process using the adhesive.

INTRODUCTION

This present invention presents new water-based adhesives suitable foruse in thermoforming lamination systems. More particularly, thisinvention presents water-based adhesive-forming compositions comprisingan aromatic polyurethane in-water dispersion or emulsion and acompatible cross-linking agent; also includable in the compositions arethickening agents and pigments. These new adhesives, it has been found,exhibit bonding strengths and temperature resistance far superior to thesolvent and water-based adhesives currently used in industrialapplications.

BACKGROUND OF INVENTION

Thermoforming or vacuum forming is essentially taking a piece ofthermoplastic sheet, heating it to a point beyond its softening point,vacuuming it to a contoured surface, and cooling the formed sheet backdown to below its softening point. A large variety of thermoplasticmaterials can be subjected to this treatment. Some of the commonmaterials used in thermoforming are listed as follows:

High Impact Polystyrene (HIPS)

Acrylonitrile-Butadiene-Styrene (ABS)

Styrene-Acrylonitrile (SAN)

Polyvinyl Chloride (PVC)

Polycarbonate (PC)

High Density Polyethylene (HDPE)

Polyphenylene Oxide (PPO) This unique forming technique has also beensuccessfully used to laminate decorative expandable vinyl covermaterials onto contoured plastic or fiberboard substrates by using aspecial class of adhesive, called thermoforming adhesives (see, e.g.Chan and Holnisch, Adhesives Age, February 1986, pp 18-20). Typically,the adhesive is first applied to the contoured part by spray, and thendried. The vinyl is then thermoformed onto this adhesive coated surface.This process has been widely used for producing high quality,domestically appealing parts for the automotive industry and furnituretrades. Some typical applications include thermoforming PVC film in themanufacture or automobile consoles, dashboards, door panels and otherinterior trim as well as in the production of decorative furniturefacings.

A variety of adhesives can be used in this process including bothorganic solvent and water-based adhesives. However, in general,solvent-based adhesives are used more extensively since such systemscure faster, exhibit higher cured bonding strengths and exhibit higher"green strengths" than their water-based counterparts. "Green strength"as used herein is the ability of the adhesive to hold two surfacestogether when first contacted and before the adhesive develops itultimate bonding properties when fully cured. The degree of greenstrength exhibited by an adhesive is very important in manyapplications, including thermoforming. High green strength adhesivestend to prevent wrinkling and slippage of films during lamination.

For these reasons, the (organic) solvent-based adhesives are thestandard adhesives used in the thermoforming industry. These solvents,however, are often flammable and/or toxic. As the regulation ofworkplace safety by federal, state, and local authorities becomeincreasingly stringent, it will become difficult, if not impossible, touse such adhesives without costly vapor collection and containmentsystems.

What is needed is an adhesive which possess the desirable properties ofthe solvent-based systems (high cured bonding strength and high greenstrength) yet, which does not exhibit the drawback of toxicity andflammability commonly encountered with the use of organic solvents.

SUMMARY OF INVENTION

It is an object of this invention to provide an adhesive which is usablein the formation of thermoformed laminates. It is further an objectiveof this invention to provide an adhesive which has a high greenstrength, high lap shear strength, high ultimate bond strength, and autility over a wide temperature range, yet which does not exhibit theproblems of toxicity and flammability commonly encountered with the useof solvent-based adhesives.

This invention presents new water-based adhesives which can be used inthermoforming lamination processes. The adhesives are characterized byexceptionally high green and ultimate bonding strength and lap shearresistance. Their bonding performance properties, in fact, are superiorto of the solvent-based and water-based standard industrial adhesivescurrently used in the thermoforming industry. Yet, being water-based,they do not exhibit the flammability and toxicity problems encounteredwhen solvent-based adhesives are used.

Each adhesive-forming composition is comprised of an aromaticpolyurethane which is emulsified or dispersed in water, and acompatible, i.e. water dispersible, cross-linking agent. The compositionof the aromtic polyurethane can vary, but at least one aromaticsubstituent must be attached to each urethane subunit; the solidscontent in the emulsion or dispersion typically ranges from 10-60%. Theamount of cross-linking agent employed must sufficient to inducecross-linking of the polyurethane, and typically ranges from 0.1 to 20%(by weight) of the composition.

The use of other polymeric compositions with the polyurethane is alsoanticipated. The adhesive-forming composition can also contain anthickening agent to increase its viscosity to a desired value or to aidin its application to the non-expandable component in a thermoforminglaminate system. While the amount will vary given the particularapplication, typically it ranges from 0.1 to 5% (by weight) of thecomposition.

Also permissible in the composition are colored pigments which can aidin the visualization of the adhesive coating during the applicationprocess. While the amount of pigment will vary given the particularpigment added and the degree of coloration desired, typically it rangesfrom 0.1 to 10% (by weight) of the total composition.

The composition of this invention can be used in a standard industrialthermoforming lamination process in place of a standard water orsolvent-based adhesive-forming composition. In such a process, theadhesive forming composition is applied to the surface to which thelaminate is to be affixed. The composition can be accomplished by anydesired means (such as brushing, dipping, roll coating, or spraying),but the preferred means, adaptable to assembly lines, is spraying.

Once applied, the compound is dried to remove the water. Again, thisdrying can be accomplished at any desired temperature, and, of course,the drying time will be increased as the temperature is lowered. Oncedried, the laminate layer can be applied by standard thermoformingmeans.

A particular benefit of the adhesives of this invention is that, due totheir stability at the high temperatures in thermoforming and high greenand ultimate bonding strength, they permit a simultaneous edge-foldingto be performed during the thermoform lamination process. Thus, theexpandable component can be laminated and edge-folded in a single step.

The laminated product, it has been found, exhibits bonding strength forsuperior to any adhesive currently in use, solvent or water-based.Furthermore, use of the water-based adhesives of this inventioneliminates the problems of toxicity and flammability often encounteredwith the use of solvent-based adhesives in thermoforming laminationprocresses. Thus, use of the adhesive compounds disclosed by thisinvention permits thermoforming lamination process to be conductedeasily and safely and produces a superior product.

DETAILED DESCRIPTION OF THE INVENTION

The base component of the adhesives of this invention is a polyurethanecomposition comprises of urethane subunits, each subunit containing oneor more aromatic substituents associated with it. This composition iscontained in water and may be either in the form of an aqueous emulsion(where water is the continuous phase) or a stabilized aqueous dispersion(again, where water is the continuous phase), wherein the term"dispersions" includes dispersions of ionomers, polymers containingpolar groups (which act as surfactants and stabilize the dispersions) assubstituents. It is anticipated that various emulsions and dispersionstabilizers and surfactants will be associated with the composition tolend stability and prevent its separation. In either case, the solidscontent can be varied given the particular composition being utilizedand the application for which it is employed; preferably, the solidscontent will range from 10 to 60% (by weight of the emulsion ordispersion).

Aromatic polyurethane emulsions and dispersions are commerciallyavailable under a variety of tradenames a representative list of suchcompound is presented below:

    ______________________________________                                        Name               Supplier                                                   ______________________________________                                        Neorez R-9431      Polyvinyl Chemicals, Inc.                                  Helastic WC-6998   Wilmington Chemical                                        Dispercoll E-584, 8299                                                                           Mobay                                                      Desmocoll E-471 (KA-8066)                                                                        Mobay                                                      QW-4476            K. J. Quinn                                                Milloxane 280      Polyurethane Specialties                                   Milloxane 5HS      Polyurethane Specialties                                   ______________________________________                                    

In addition to these, any number of aromatic polyurethane-in-wateremulsions and dispersions will be suitable for incorporation into theadhesives of this invention. Also, blending of other polymers such asnitriles, arcylates, etc. with the polyurethane system to lower costs ispossible.

The only other active component in the adhesives of this invention isthe cross-linking agent. This agent is responsible for the hightemperature resistance and high bond strength properties of thesecompositions, which arise due to the cross-linking of the polyurethanecomponents. For the invention to be effective, the cross-linking agentmust be water-dispersible and stable in the presenceof water to have apractical pot-life as the application dictates; yet it must also becapable of inducing cross-linking at room temperature. Furthermore, thecross-linking must occur at a rate sufficiently slow to permit thecomposition to remain stable prior to use (i.e. the time between theinitial mixing and when the cross-linking reaches a point such that theadhesive properties are lost, must be long), yet not so slow as to havean undesirably low ultimate bond strength.

One class of compounds which meet these criteria are organicisocyanates, particularly the aliphatic polyisocyanates. While many ofthese compounds are water-reactive, others can be readily dispersed inwater and will exhibit desirable cross-linking properties. Suchcompounds are available under a variety of tradenames including but notlimited to, the following:

    ______________________________________                                        Name                 Supplier                                                 ______________________________________                                        Desmodur KA-8365     Mobay                                                    Rubinate MF-178 (modified                                                                          Rubicon Chemical                                         methylene diisocyanate)                                                       Isocet Cx-10         Ashland                                                  ______________________________________                                    

Each of these isocyanates are free, i.e., unblocked, polyisocyanateswhich are stable in the presence of water. The water stability of thesecompounds is demonstrated below by open time and pot life studies.Specifically, Desmodur KA-8365 is a polymeric isocyanate of a modifiedaliphatic isocyanate based on hexamethylene diiisocyanate (100%);Rubinate MF-178 comprises about 48% by weight 4,4'-diphenyl methanediisocyanate ("MDI"), 48% of oligomers of similar structures, and 4% ofmodified MDI; and Isoset CX-10 is a polymeric MDI type diisocyanatewhich also contains solvents. Other cross-linking agents exhibitingsimilar properties can also be utilized.

The precise concentration of the cross-linking agent in the overallcomposition will vary given the particular agent utilized and theapplication for which it is employed. Preferably, the concentration willrange from 0.1 to 20% (by weight) of the total composition.

For certain applications, it may be advantageous to have a higherviscosity composition. Such increased viscosity can be a definiteadvantage when, for example, the adhesive forming composition is appliedto a sloped or vertical surface, since it will reduce its tendency torun-off.

For these applications, a viscosity-increasing agent in the form ofthickener can be compounded into the adhesives of this invention. Suchcompounds can be utilized to increase the viscosity of theadhesive-forming composition to a desired level. While the amount ofthickener in the composition will vary given the particular application,it preferably ranges from 0.1 to 5% (by weight) of the composition.

One class of thickeners useful in these compositions are acrylatethickeners such as Acrysol S and Acrysol TT 678 of Rohm and Haas, andRES 6038 of Union 76. A wide range of other thickeners compatible withthe compositions are available under a variety of tradenames. Theseinclude, but are not limited to, the following:

    ______________________________________                                        Name                Supplier                                                  ______________________________________                                        QP1500              Union Carbide                                             Collacral VL        BASF                                                      ______________________________________                                    

Other thickeners compatible with the system can also be used.

In some applications, it may be particular advantageous to visualize theadhesive forming composition. This is particularly important if theadhesive is used in a thermoforming lamination process and the panelsare visually inspected to determine if the adhesive is evenly applied.

For these applications, pigments can be incorporated into thecompositions. Virtually any compatible pigment can be used, the maincriterion being that it remain unreactive with the other adhesivecomponents. While the precise quantity of pigment added will be dictatedby the actual compound used and the degree of coloration desired, itpreferably will range from 0.1 to 10% of the composition.

A wide variety of compatible pigments are available commercially for usein this invention. These include, but are not limited to, the Flexiversepigments marketed by Sun Chemical under the following designations:

    ______________________________________                                        Color          Product                                                        ______________________________________                                        Black          Flexiverse Black LFD-4343                                      Red            Flexiverse Red RFD-                                                           3217, RWD-1170, RFD-5104,                                                     RFD-4347                                                       Blue           Flexiverse Blue BFD-1149                                       ______________________________________                                    

The adhesive-forming compositions of this invention are preferablyprepared in two parts: Part A contains the aromatic polyurethaneemulsion (or dispersion) and the thickener and pigment (if any); Part Bcontains the cross-linking agents. Immediately prior to use (or as closeto this time as practical) the two parts are mixed at room temperatureand the blended composition is applied to the desired surface.

In a preferred embodiment of this invention, the composition iscomprised of the following:

    ______________________________________                                                                     Part                                             Ingredients    Supplier      (by weight)                                      ______________________________________                                        PART A                                                                        Neorez R-9431  Polyvinyl Chemical                                                                          100.0                                            (a 35% solids content                                                         aromatic polyurethane                                                         in water emulsion)                                                            Acrysol TT-678 Rohm & Haas   0.5                                              (an acrylate thickener)                                                       Flexiverse Black                                                                             Sun Chemical  0.1                                              LFD 4343 (a carbon                                                            black pigment)                                                                               Total:        100.6                                            PART B                                                                        Desmodur KA-8365                                                                             Mobay         5.0                                              (a solvent free aliphatic                                                     polyisocyanate)                                                               ______________________________________                                    

Neorez 9431 is an emulsion of a polyester based aromatic urethane. It isan anionic material containing carboxylic and uea moeities rather thanhydroxyl groups. These carboxylic and urea moeities react slower thanhydroxyl groups, so that the material has a longer open time. The Neorez9431 has a tensile strength of about 3500 psi, a 100% modulus of about1160 psi and a molecular weight of approximately 125,000.

When parts A and B are mixed, the composition has a high green strength,and has a pot-life in excess of 7 hours. Furthermore, the viscosity ofthe composition is sufficiently high to permit application by brushing,yet low enough to permit spray application. In thermoforming laminationprocesses, also characterized by its high green strength, high lap shearstrength, high ultimate bonding strength, and wide service temperature,which covers a wide range from -22° F. to 212° F. This adhesive alsopermits for edge trimming and folding immediately after removal forthermoforming equipment. In addition, it permits simultaneousedge-folding during the thermoforming process (allowing for a one-stopprocess) due to its high green and ultimate bond strengths. This processis important in the automotive industry and has heretofore been possibleonly with solvent based adhesive. Its adhesive performance is, thus,superior to that of current industrial standard adhesives, both solventand water-based.

The adhesive-forming compositions of this invention can be employed inplace of the water and solvent-based adhesives currently used byindustry in such standard processes. The compositions of this inventionwill form laminates of particularly high bonding strength, yet do notexhibit the toxically and flammability problems commonly encounteredwith solvent-based adhesives.

When employed in such a process the blended adhesive forming composition(Parts A and B) of this invention is applied to the surface of thenon-expandable (rigid) component. Being water-based, the composition iscompatible with a variety of substances including wood, particle boards,chipboards, and most plastics. Once applied, the water is removed bydrying, either at room temperature or elevated temperature. While dryingcan be accomplished at any temperature, the drying temperature should bechosen based on the properties of the adhesive composition (i.e., itspot life and its thermal stability) as drying at lower temperaturesrequires longer times. For the preferred adhesive described in section4.1.5, the drying can be accomplished by incubating the composition for5-30 minutes at room temperature, followed by incubation in an oven at100° C. for 2-15 minutes.

Once the adhesive has dried, the lamination can be accomplished bystandard thermoforming means. The final product is a laminate ofunusually high bond strength and peel/lap-shear resistance.

EXAMPLES

In order to illustrate the properties of the water-based thermoformingadhesive, a Rohm and Haas 2 part acrylic water-based adhesive(E-2128/2129) was used. For each test, the adhesive was preparedaccording to the manufacturers directions and a thin coat of adhesivewas brushed or sprayed to the rough side of a flat Royalite R-20 ABSpanel. It was allowed to air dry at room temperature for 5-25 minutes,and then oven dried at 170°-220° F. for 5 minutes. A vinyl sheet washeated to 310°-320° F. and then vacuum formed onto the adhesive coatedside of the ABS panel.

The panels were then examined for peel and lap shear in accordance withthe procedures set forth in ASTM procedures D-413 (peel) and D-816(lap-shear). Briefly, 1" wide strips were cut for the peel testing and1" squares were used for lap testing. Testing was accomplished on anInstron tensile strength tester with the jaw speed set at 2"/min; forthe peel test, the 180° peel mode was used. Tests were conducted afterincubation at room temperature (25° C.) for the specified amount oftime; the samples were than examined either at 25° C. or heated to 100°C. immediately prior to testing. The results are summarized in Table I.

                  TABLE I                                                         ______________________________________                                        Test @ 2 in./min.                                                                          25° C.                                                                             100° C.                                       ______________________________________                                        180° Peel                                                                             Test Result (lb./in width)                                     Incubation                                                                    Initial @ RT   3.8 CF        --                                               24 hrs. @ RT   4.0 CF        0.9 CF                                           3 Days @ RT    --            0.6 CF                                           7 Days @ RT    --            0.4 CF                                            Lap Shear     Test Result (lb./in..sup.2)                                    Incubation                                                                    Initial @ RT   20.5 CF       --                                               24 hrs @ RT    --            3.5 CF                                           3 Days @ RT    --            4.0 CF                                           7 Days @ RT    --            3.0 CF                                           ______________________________________                                         CF indicates cohesive failure of the adhesive                            

As shown, the adhesive exhibited cohesive failure in all tests. Sincecohesive failure is evidence of a lack of structural integrity (theadhesive was found on both the panel surface and the laminate), theadhesive is relatively weak and any laminate can be easily removed.

The adhesive was initially prepared in two parts. Part A was prepared asa mixture of:

    ______________________________________                                        100 parts   Neorey R-9431 (solids content 35%)                                (by wt)                                                                       0.5 parts   Acrysol TT-678                                                    0.1 parts   Flexiverse Black LFD 4343                                         ______________________________________                                    

Part B was Demodur KA 8365.

Prior to each experimental series, the parts were combined in the ratio5 parts B/100 parts A and stirred 10-20 minutes at room temperature.Unless otherwise specified, the adhesive was then immediately applied tothe test panels, after which the water was removed by drying for about 5minutes at room temperature and an additional 5 minutes in an oven at100° C.

Laminates were unless otherwise stated, prepared immediately after thedrying.

The adhesive prepared in example 5.2 was subjected to the lap and peeltests following the procedure described in example 5.1. The results arepresented in Table II.

                  TABLE II                                                        ______________________________________                                        Test @ 2 in./min.                                                                          25° C.                                                                             100° C.                                       ______________________________________                                        180° Peel                                                                             Test Result (lb./in width)                                     Incubation                                                                    Initial @ RT   16.0 AF       --                                               24 hrs. @ RT   26.0 VT       3.3 AF                                           3 Days @ RT    --            3.6 AF                                           7 Days @ RT    --            3.4 AF                                            Lap Shear     Test Result (lb./in..sup.2)                                    Incubation                                                                    Initial @ RT   32.0 VT       --                                               24 hrs. @ RT   --            7.3 AF                                           3 Days @ RT    --            6.8 AF                                           7 Days @ RT    --            8.9 VT                                           ______________________________________                                         AF = Adhesive Failure                                                         VT = Vinyl Tear                                                          

As shown, the adhesive did not exhibit cohesive failure in any trial,and was stable to much higher peel and shear forces than the example 5.1adhesive. When failure did occur, the mode was always either an adhesivefailure (where the adhesive remains bound to the Royalite panel) or bytearing the vinyl laminate. Both of these failure modes attest to thehigh degree of structural integrity of the adhesive.

For this example, the adhesive of Example 5.2 was prepared without theinclusion of Part B; all other procedures remained the same. The resultsof the peel and lap tests are presented in Table III.

                  TABLE III                                                       ______________________________________                                                      25° C.                                                                        100° C.                                           ______________________________________                                        180° Peel                                                                              Results (lb./in. width)                                       Incubation                                                                    Initial @ RT    16.0 AF  --                                                   24 hrs. @ RT    19.0 VT  1.3 CF                                               3 Days @ RT     --       1.0 CF                                               7 Days @ RT     --       1.0 CF                                                Lap Shear      Results (lb./in.sup.2)                                        Incubation                                                                    Initial @ RT    34.0 VT  --                                                   24 hrs. @ RT    --       4.4 CF                                               3 Days @ RT     --       4.0 CF                                               7 Days @ RT     --       4.0 CF                                               ______________________________________                                    

The results clearly demonstrate that the inclusion of polyisocyanate(component B) is necessary for the high temperature performance, asevidenced by the cohesive failures observed in the 100° C. trials.

This test series was conducted on the base composition described inexample 5.2, containing varying amounts of polyisocyanate (Part B). Thesamples were prepared as described in 5.2, and incubated at roomtemperature for the indicated amount of time. The results are presentedin Table IV.

                                      TABLE IV                                    __________________________________________________________________________    Polyisocyanate Level                                                          (parts/100 part)                                                                          0   1 3   4   5   6   8                                           __________________________________________________________________________    180° Peel                                                              Incubation                                                                    Sample Condition                                                              Test Temp   Results (lb./in. width)                                           Initial                                                                             25° C.                                                                       16  18                                                                              15  16  16  13  14                                          24 hr.                                                                              25° C.                                                                       19 VT                                                                             --                                                                              19 VT                                                                             25 VT                                                                             22 VT                                                                             22 VT                                                                             --                                          24 hr.                                                                              100° C.                                                                      1.3 --                                                                              2.4 2.5 3.3 2.9 --                                          7 Days                                                                              100° C.                                                                      1.0 --                                                                              3.4 3.0 3.4 3.0 --                                          Lap Shear                                                                     Incubation                                                                          Test Temp                                                                           Results (lb./in..sup.2)                                           Initial                                                                             25° C.                                                                       34  --                                                                              37 VT                                                                             36 VT                                                                             32 VT                                                                             35 VT                                                                             --                                          24 hr.                                                                              100° C.                                                                      4.4 --                                                                              6.8 6.5 7.3 7.6 --                                          7 Days                                                                              100° C.                                                                      4.0 CF                                                                            --                                                                              7.5 VT                                                                            7.5 VT                                                                            8.9 VT                                                                            5.0 VT                                                                            --                                          __________________________________________________________________________

As shown, all compositions exhibited a high strength, even at 1%polyisocyanate; the only cohesive failure was observed in the lap sheartest for the 0% sample (note: where the failure mode is not specified,the failure was predominantly via adhesive failure).

The force values in Table IV suggest that a wide range of polyisocyanatelevels can be used in accordance with this invention to improve the hightemperature performance of the polyurethane composition. The data alsosuggests that the optimum level is 5 parts Part B per 100 parts of PartA.

This test series was conducted to assess the performance of the adhesiveas a function of time (pot life) after polyisocyanate is added. Thesample was prepared as described in Example 5.2. Peel and shear sampleswere prepared and conditioned in the same fashion discussed in Example5.1, except that fiberboard panels were substituted for the Royalite ABSones. The results are presented in Table V:

                                      TABLE V                                     __________________________________________________________________________    Hours After Mixing                                                                         1    2    3    4    5    6    7                                  __________________________________________________________________________    180° Peel                                                              Sample Condition/Tested                                                       Incubation                                                                    (at RT)                                                                             Test Temp                                                                            Results (lb./in. width)                                          24 hr.                                                                              25° C.                                                                        8.2 FT                                                                             5.0 FT                                                                             5.6 FT                                                                             7.2 FT                                                                             5.6 FT                                                                             7.4 FT                                                                             6.0 FT                             24 hr.                                                                              100° C.                                                                       2.3 FT                                                                             3.1 FT                                                                             2.3 FT                                                                             3.0 FT                                                                             2.2 FT                                                                             2.3 FT                                                                             2.1 FT                             15 days                                                                             100° C.                                                                       3.6 FT                                                                             3.4 FT                                                                             2.6 FT                                                                             2.8 FT                                                                             2.8 FT                                                                             2.5 FT                                                                             1.9 FT                             (Lap Shear.sup.2)                                                             Incubation                                                                    (at RT)                                                                             Test Temp                                                                            Results (lb./in..sup.2)                                          24 hr.                                                                              25° C.                                                                        38.5 VT                                                                            32.0 VT                                                                            32.0 VT                                                                            33.0 VT                                                                            35.5 VT                                                                            36.5 VT                                                                            34.0 VT                            24 hr.                                                                              100° C.                                                                       7.1 FT                                                                             8.5 FT                                                                             8.9 FT                                                                             8.8 FT                                                                             10.0 FT                                                                            8.6 FT                                                                             7.9 VT                             15 days                                                                             100° C.                                                                       8.6 FT                                                                             9.4 VT                                                                             7.8 VT                                                                             8.4 FT                                                                             8.4 VT                                                                             7.0 VT                                                                             7.2 VT                             __________________________________________________________________________     FT = Fiber Tear (a tear in the fiberboard panel)                         

The results reveal that even 7 hours after blending, the adhesive stillperforms well, exhibiting high bonding strength.

This test series was conducted to assess the performance of the adhesiveas a function of open time (time elapsed after the adhesive has beendried and before thermoforming). The adhesive was prepared as describedin example 5.1. Peel samples were prepared and conditioned at roomtemperature for 24 hours in the same fashion discussed in Example 5.1.The 800 peel test results are presented in Table VI:

                  TABLE VI                                                        ______________________________________                                        Open Time (hours)                                                                          25° C. Results (lb/in width)                                                              100° C.                                ______________________________________                                        0.5          18.3 VT            1.6 AF                                        1.0          21.3 VT            1.7 AF                                        2.0          18.0 VT            2.2 AF                                        3.5          15.0 VT            1.8 AF                                        5.0          22.0 VT            2.0 AF                                        ______________________________________                                    

As shown, the bonding strength remains high, even after 5 hours.

This test series was conducted to assess the adhesive performance thebonded finished laminate; the finished laminate system was subjected tothe following heat cycles:

    ______________________________________                                        Cycle A      21/2 hr. @ 100° F. (38° C.)/100% RH                             21/2  hr. @ -22° F. (-30° C.)                                   3 hr. @ 212° F. (100° C.)                          Cycle B      3 hr. @ 200° F. (93° F.)                                        21/2  hr. @ 100° F. (38° C.)/100% RH                            21/2  hr. @ -20° F. (-29° C.)                      ______________________________________                                    

The adhesive was prepared as described in Example 5.2. Peel and shearsamples were prepared in the same fashion discussed in Example 5.1,except that an ABS door panel was used under actual productionconditions; the bonded system were incubated room temperature for 24hours prior to testing and all tests were conducted at room temperature.Tests results are summarized in Table VII:

                  TABLE VII                                                       ______________________________________                                                     25° C. Results                                                                  100° C. Results                                  ______________________________________                                        180° Peel (lb./in.)                                                    Control        15.6 VT    2.4                                                 Cycle A        14.0 VT    0.8                                                 Cycle B        13.5 VT    0.9                                                 Lap Shear (lb./in..sup.2)                                                     Control        27.0 VT    8.0                                                 Cycle A        31.0 VT    5.4                                                 Cycle B        27.0 VT    5.8                                                 ______________________________________                                    

As shown, the adhesive performed satisfactorily after being exposed toboth cycles (note: where failure mode is not specified, it waspredominantly via adhesive failure).

For comparison purposes, a similar experimental was conducted on asolvent-based standard industrial adhesive which has been successfullyused in the manufacture of consoles, dashboards, door panels forautomotive and furniture facings, 3M PB 4801 Adhesive. The testconditions were the same as above and the results are presented in TableVIII:

                  TABLE VIII                                                      ______________________________________                                                     25° C. Results                                                                  100° C. Results                                  ______________________________________                                        180° Peel (lb./in.)                                                    Control        7.5        1.3                                                 Cycle A        3.7        0.9                                                 Cycle B        5.0        1.0                                                 Lap Shear (lb./in..sup.2)                                                     Control        33.0 VT    5.6                                                 Cycle A        28.5 VT    5.5                                                 Cycle B        30.0 VT    4.8                                                 ______________________________________                                    

A comparison of the bonding strength data reveals that the water-basedsolvent of this invention, performs better than a standard solvent-basedadhesive under the same conditions.

To assess the effect of prolonged standing after blending, two samplesof adhesive were prepared as described in section 5.2, and the viscosityof each was measured periodically on a RVF Brookfield Viscometer at 74°F. using a number 4 spindle at 10 rpm. The viscosity of the first samplewas measured without any modification, while the second sample wasagitated prior to the measurement. The results are presented in TableIX:

                  TABLE IX                                                        ______________________________________                                        Viscosity Study                                                               Brookfield Viscosity (CPS)                                                    Incubation Time RT                                                                           A           B                                                  (Hours)        Without Mixing                                                                            With Mixing                                        ______________________________________                                        0              2,000       1,700                                              1              3,700       2,300                                              2              4,500       --                                                 3              6,400       2,800                                              4              8,500       2,500                                              5              8,800       2,700                                              6              9,400       --                                                 7              10.400      --                                                 Overnight      17,500      3,000                                              ______________________________________                                    

The results demonstrate the viscosity of the adhesive and, thus, thesprayability of material remains relative constant throughout pot lifewith mixing. Thus, the adhesive acts like a thixotrope and agitationwill reduce viscosity.

The effect of variation in drying time and temperature was examined inthis test series. Briefly, the adhesive was prepared as described insection 5.2, and was applied to fiberboard panes. Each panel was thensubjected to a different drying condition, after which PVC wasthermoform laminated onto the coated surfaces. After a 24 hourincubation at ambient temperature, the laminates were subject to the180° Peel test. The results are summarized in Table X:

                  TABLE X                                                         ______________________________________                                              Temp.    Time    Adhesive Wet Wt.                                                                           RT Peel                                   Sample                                                                              (° F.)                                                                          (Min.)  (gm/100 sq. in)                                                                            (lb./in width)                            ______________________________________                                        A     200      2       5.8          1.3 FT                                    B     200      4       7.8          0.7 FT                                    C     200      6       6.8          1.3 FT                                    D     190      2       6.0          0.7 FT                                    E     190      4       7.1          0.9 FT                                    F     190      6       6.0          1.1 FT                                    G     170      2       6.2          1.1 FT                                    H     170      4       6.1          0.9 FT                                    I     170      6       6.7          0.4 FT                                    J     150      2       7.0          1.4 FT                                    K     150      4       6.7          0.3 FT                                    L     150      6       7.1          0.9 FT                                    ______________________________________                                    

As shown, over the wide range of drying times and temperatures examined,the adhesive exhibited high bond strength as evidenced by the fibertears observed.

It is apparent that many modifications and variations of this inventionas hereinabove set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only, and the invention is limited only by the terms of theappended claims.

What is claimed is:
 1. A method of joining an expandable and anon-expandable component which comprises:(a) applying to thenon-expandable component, an adhesive forming composition comprising (i)an aqueous aromatic polyurethane emulsion or dispersion comprising apolyurethane compound of repeating urethane subunits, each having atleast one aromatic substituent associated therewith; (ii) an effectiveamount of a cross-linking agent which is water-dispersible and stable inthe presence of water yet being able to induce cross-linking of thepolyurethane at room temperature at a rate sufficient to permit thecomposition to form an adhesive haaving suitable ultimate bond strengthand green strength; and (iii) a sufficient solids content to enable theresultant polyurethane to join and hold said components together; (b)drying the applied adhesive forming composition to remove the water; and(c) joining the expandable component to the surface coated with thedried adhesive by a thermoforming lamination process.
 2. The method ofclaim 1 wherein the drying is performed at ambient temperature.
 3. Themethod of claim 1 wherein the drying is performed at an elevatedtemperature.
 4. The method of claim 1 wherein the drying is performed inan oven at 100° C.
 5. The method of claim 1 further comprisingedgefolding the expandable component during the thermoforming laminationprocess.
 6. A method of joining an expandable component and anon-expandable component which comprises:(a) applying to thenon-expandable component an adhesive-forming composition comprising:(i)an aqueous aromatic polyurethane emulsion or dispersion comprising apolyurethane compound of repeating urethane subunits, each having atleast one aromatic substituent associated therewith; (ii) an effectiveamount of a cross-linking agent of a solvent-free, water-dispersible,organic isocyanate compound which is stable in the present of water andis able to induce cross-linking of the polyurethane at room temperatureat a rate sufficient to permit the composition to form an adhesivehaving suitable ultimate bond strength and green strength; and (iii) asufficient solids content to enable the resultant adhesive to join andhold said components together; (b) drying the applied adhesive formingcomposition to remove the water; and (c) joining the expandablecomponent to the surface coated with the dried adhesive by athermoforming lamination process.
 7. The method of claim 6 wherein theemulsion or dispersion has a solids content ranging from 10-60%, andwherein the amount of cross-linking agent is between 0.1 and 20% byweight of the composition.
 8. The method of claim 6 wherein the dryingis performed at ambient temperature.
 9. The method of claim 6 whereinthe drying is performed at an elevated temperature.
 10. The method ofclaim 6 further comprising edgefolding the expandable component duringthe thermoforming lamination process.
 11. A method of joining anexpandable component and a non-expandable component which comprises:(a)applying to the non-expandable component an adhesive-forming compositioncomprising:(i) an aqueous aromatic polyurethane emulsion or dispersioncomprising a polyurethane compound of repeating urethane subunits, eachhaving at least one aromatic substituent associated therewith; (ii) across-linking agent in an amount of between 0.1 and 20%, by weight ofthe composition, of a solvent-free, water-dispersible organic isocyanatecompound which is stable in the present of water and is able to inducecross-linking of the polyurethane at room temperature at a ratesufficient to permit the composition to form an adhesive having suitableultimate bond strength and green strength; (iii) between 0.1 and 5%, byweight of the composition, of a thickener to increase the viscosity ofthe composition; (iv) between 0.1 and 10%, by weight of the composition,of a pigment to impart a color to the composition; and (v) a solidscontent of between 10 and 60% to enable the resultant adhesive to joinand hold said components together; (b) drying the applied adhesiveforming composition to remove the water; and (c) joining the expandablecomponent to the surface coated with the dried adhesive by athermoforming lamination process.
 12. The method of claim 11 wherein thethickener is an acrylate and wherein the organic isocyanate compound isan aliphatic polyisocyanate.
 13. The method of claim 11 wherein thedrying is performed at ambient temperature.
 14. The method of claim 11wherein the drying is performed at an elevated temperature.
 15. Themethod of claim 11 further comprising edgefolding the expandablecomponent during the thermoforming lamination process.
 16. Athermoformed laminate article comprising a non-expandable layer, anexpandable laminate member situated on the surface of the non-expandablelayer, and a cross-linked polyurethane adhesive situated between the twomembers, wherein the adhesive is obtained from an adhesive formingcomposition comprising:(a) an aqueous aromatic polyurethane emulsion ordispersion comprising a polyurethane compound of repeating urethanesubunits, each having at least one aromatic substituent associatedtherewith; (b) an effective amount of a cross-linking agent to inducecross-linking, which agent is water-dispersible and stable in thepresence of water yet being able to induce cross-linking of thepolyurethane at room temperature at a rate sufficient to permit thecomposition to form an adhesive having suitable ultimate bond strengthand green strength; and (c) a sufficient solids content to enable theresultant adhesive to join and hold said components together.
 17. Athermoformed laminate article comprising a non-expandable layer, anexpandable laminate member situated on the surface of the non-expandablelayer, and a cross-linked polyurethane adhesive situated between the twomembers, wherein the adhesive is obtained from an adhesive formingcomposition comprising:(a) an aqueous aromatic polyurethane emulsion ordispersion comprising a polyurethane compound of repearing urethanesubunits, each having at least one aromatic substituent associatedtherewith; (b) an effective amount of a cross-linking agent of asolvent-free, water-dispersible, organic isocyanate compound which isstable in the present of water and is able to induce cross-linking ofthe polyurethane at room temperature at a rate sufficient to permit thecomposition to form an adhesive having suitable ultimate bond strengthand green strength; and (c) a sufficient solids content to enable theresultant adhesive to join and hold said components together;
 18. Athermoformed laminate article comprising a non-expandable layer, anexpandable laminate member situated on the surface of the non-expandablelayer, and a cross-linked polyurethane adhesive situated between the twomembers, wherein the adhesive is obtained from an adhesive formingcomposition comprising:(i) an aqueous aromatic polyurethane emulsion ordispersion comprising a polyurethane compound of repeating urethanesubunits, each having at least one aromatic substituent associatedtherewith; (ii) a cross-linking agent in an amount of between 0.1 and20%, by weight of the composition, of a solvent-free, water-dispersibleorganic isocyanate compound which is stable in the present of water andis able to induce cross-linking of the polyurethane at room temperatureat a rate sufficient to permit the composition to form an adhesivehaving suitable ultimate bond strength and green strength; (iii) between0.1 and 5%, by weight of the composition, of a thickener to increase theviscosity of the composition; (iv) between 0.1 and 10%, by weight of thecomposition, of a pigment to impart a color to the composition; and (v)a solids content of between 10 and 60% to enable the resultant adhesiveto join and hold said components together.